Insulating materials made from nonwoven materials are well known that are suitable for use in structures such as buildings, appliances, and automotive applications to provide thermal and/or acoustical insulation. Depending on the desired features required of the end-product, such nonwoven materials have been made from various constituents.
One such nonwoven material is made using cellulose fibers, with or without blends of other fibers, and typically requires some sort of binder. Such cellulose-containing insulating materials are typically made using dry- or air-laid processes, that is, by typical papermaking processes, and the binder is applied as a spray or foam. It is also possible to add other fibers to aid in binding the cellulose fibers, which are activated and cured by heat to help form the nonwoven material.
It is also well known to make such insulating materials with synthetic fibers, such as polyester fibers. It is possible to make these materials using wet-laid processes. Such insulating materials typically include water-based binders, typically in the form of a latex binder, which are added to the process to ensure adhesion of the fibers. The binder is typically sprayed on, beater added or saturated with a binder solution. Generally, from about 4% to about 35% binder material is employed. Applying latex binder, by for instance spraying the binder onto one or more surfaces of the nonwoven web, can result in a thickness of latex binder buildup on the surface, which lends towards unwanted stiffness of the web. Further, binder migration can occur, meaning that the latex binder moves through the sheet unevenly, and pools, for instance, at outer edges thereof.
In addition, many gasket manufacturers have moved away from conventional die cutting and replaced these systems with more modern water jet cutting systems. These systems are significantly more productive and profitable than their die cutting counterparts. Unfortunately water jet cutting can present technical complications when handling nonwoven materials that include refractory fibers. Examples of typical refractory fibers include ceramic fibers and manmade vitreous fibers. Such refractory fibers are extremely hydrophilic and have a tendency to soak up tremendous amounts of liquid, typically water, for their mass. During the water jet cutting process, a water laden nonwoven material including such refractory fibers is capable of absorbing enough water to sufficiently compromise the mechanical strength of the material. This loss in strength can lead to downstream process issues and increased scrap.
In materials made from synthetic and/or cellulose fibers, the non-binder fibers typically make up the largest portion of the material. That is, the cellulose and synthetic fibers are used as the main portion of the nonwoven material, typically making up over 50 wt. % of the overall composition, which is expensive to make.
It is also known to make nonwoven webs using glass and/or ceramic fibers. As would be understood by one of ordinary skill in the art, during production of ceramic fibers, for instance, relatively large ceramic beads, known as “shot,” may be pulled into the ceramic fiber material. While the thus-produced shot has the same chemical makeup of the ceramic fibers, the resulting structures and functionality in use are markedly different. Such shot are typically considered undesirable in the nonwoven material because such shot tend to conduct heat more readily than the thin ceramic fibers and generally lead to uneven distribution of the ceramic fibers across the resulting nonwoven web or material. Various attempts have been made to produce nonwoven webs with minimum shot, but such methods have typically employed air-laid, needling and/or gravity-laid processes, typically with the addition of a latex binder or binder fiber. Many advantages can be found in wet-laid structures, as compared to structures made from these other processes, including but not limited to the ability to form lower basis weight materials having uniform distribution of fibers and favorable density, without breaking fibers. This leads to improvements in strength and thermal properties, to name a few. Additionally, it is simply difficult to make thick glass-/ceramic-fiber-based media using such processes. In fact, as would be understood by one of ordinary skill in the art, such processes are typically capable of making useful glass-/ceramic-fiber-based media with thicknesses around 1/32 inch (0.8 mm), and typically no greater than about 0.125 inches (3.175 mm), without resulting in cracking of the media. When used in appliances, such glass-/ceramic-fiber-based media advantageously take the form of various products including but not limited to parting paper, gasketing material, hot-spot management materials, and the like.
Yet another problem identified with using ceramic fibers is the potential for such fibers to become airborne and to become carcinogenic if inhaled. The European Community (EC) classified Refractory Ceramic Fiber as a carcinogen 2 in 1997, and the classification came into effect in 2007. Carcinogen 2 is class 1B material under the EC's Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulations, or a “Substance of very high concern.”
Addition of latex binders and/or binder fibers to nonwoven webs also has known problems. A non-limiting example of a binder fiber is a PVOH binder fiber, (which essentially dissolves when processed and dries in a similar fashion to a latex binder). As used herein, the term “binder fibers” excludes thermoplastic fibers, e.g., “monocomponent fibers,” and “bicomponent fibers”, as defined in greater detail hereinbelow. In the case where the latex binders are added using a sprayed-on method results in abysmal latex yield, meaning that much of the latex is essentially washed-out in the process. Thus, costs of raw materials are needlessly higher, as are the clean-up costs of removing the latex from the wastewater to abate environmental issues. Furthermore, latex binders and/or binder fibers are not always evenly distributed, leading to material frailty and manufacturing difficulty. Thus, minimizing, or even eliminating latex binders and/or binder fibers is desirable.
Although addition of thermoplastic bicomponent fibers, that is fibers typically having a core and a sheath, typically having differing melting points, in addition to or in place of the latex binder are known, there are problems associated therewith, particularly when attempting to incorporate such bicomponent fibers using a wet-laid process. One such problem has been achieving a uniform dispersion of the bicomponent fibers in the resulting nonwoven material.
With reference to FIG. 1, a wet-laid nonwoven web 10 according to the prior art is depicted in a highly stylized fashion. The web 10 was made from a wet-laid process in which, for instance, ceramic fibers 12 containing shot 16, as supplied from the manufacturer, (e.g. not cleaned to remove shot), is wet-laid to form the nonwoven web 10. Upon formation of the nonwoven web 10, binder, for instance latex binder, is sprayed onto the web and dried. As shown herein, the binder forms bonding points 18 between the ceramic fibers 12 and/or the shot 16.
In view of the disadvantages associated with currently available insulating materials, there remains a need for a material that minimizes or eliminates use of such binder additives, while maintaining desired properties, that is, sustains the form and strength of the material without becoming too stiff, and having a better raw material yield than previous methods. It may be advantageous in some applications to also impart a degree of water repellency to the nonwoven material.